In both open and endoscopic surgeries, it often is necessary to seal, weld or cauterize blood vessels or other vascularized tissues. For example, in subfacial endoscopic perforator surgery (SEPS), a perforator vessel in a patient's leg is sealed or welded closed to alleviate the effects of a venous ulceration. In a typical SEPS procedure, the surgeon uses a mechanically deformable clip to pinch off the perforator vessel. Because a single clip may not seal the vessel reliably, multiple clips typically are used to assure an effective seal. It would be preferable to seal a vessel without leaving such metal clips implanted in the patient's body.
Ultrasound and radiofrequency devices have been developed for sealing blood vessels but such devices often will not create a secure seal, particularly when used on larger diameter blood vessels. Previously known commercially available ultrasound devices suffer from the disadvantage of being slow to deliver sufficient energy to seal a blood vessel. In addition, ultrasound devices generally are capable of thermally treating only a narrow band across a target blood vessel (due to the focused nature of the ultrasound beam), and thus may not provide a reliable seal. To improve the chances of a permanent seal, surgeons often apply ultrasound energy at multiple locations along a blood vessel, a practice that is inconvenient and time-consuming.
Previously known commercially available RF instruments for sealing blood vessels deliver energy more quickly than ultrasound devices. A typical previously known RF bi-polar grasper, suitable for such procedures, is described with respect to FIGS. 1A and 1B. Such an instrument may be used to seal a blood vessel by squeezing the vessel between the opposing jaw faces of the grasper while applying an RF current (FIG. 1B). Each jaw face comprises a conductive electrode (first electrode 2A and second electrode 2B) and when operated in a bi-polar mode, RF current flows directly "across" vessel 3 in the direction indicated by the arrow in FIG. 1B between first electrode 2A and second electrode 2B.
The integrity of the sealing effect achieved with the device of FIGS. 1A and 1B is greatly influenced by the conductive characteristics of the target tissue. For example, the impedance of the tissue of the vessel walls and endothelium changes continuously during the application of RF energy. Impedance typically increases quickly during energy application until the bi-polar RF energy flow is impeded or restricted altogether. Often this will occur before the vessel walls around the lumen are fused in a uniform manner. Effective sealing of the vessel therefore depends on providing an appropriate energy delivery profile (i.e., energy level delivered to the tissue over an appropriate time interval) to cause fusion of molecules within a targeted region, with little or no charring or carbonization.
Because tissue impedance is an uncontrolled variable when using previously known methods and apparatus, the effectiveness of such previously known tissue welding apparatus and methods can be highly variable. It is for this reason that previously known commercially available RF devices have not provided reliable sealing for large blood vessels.
It would therefore be desirable to provide methods and apparatus, preferably utilizing RF energy, that control the effects of tissue impedance to provide an effective energy delivery profile in tissue targeted for welding.
It further would be desirable to provide methods and apparatus that control the effects of tissue impedance to reduce charring of tissue and the creation of smoke in an endoscopic workspace.